1. Technical Field
This invention is related to the field of internal combustion engine systems and control. More particularly, it is related to an exhaust gas re-circulation control used to reduce NOx emissions in an internal combustion engine.
2. Discussion
The prior art includes a variety of conventional methods for detecting and using ionization current in a combustion chamber of an internal combustion engine. However, each of the various conventional systems suffers from a great variety of deficiencies. For example, prior art ionization current detection circuits are generally too slow and generate a current signal with low signal-to-noise ratio.
Exhaust gas re-circulation is an effective way to reduce NOx emissions in an internal combustion engine. The exhaust gas recirculation widely used in the prior art is calibrated using engine mapping points. That is, the desired exhaust gas re-circulation rates used in controlling an engine are mapped to various engine operating conditions such as load and speed. Due to engine to engine variation, engine aging, and engine operational environmental variation, open-loop calibration of a desired exhaust gas re-circulation rate is very conservative.